Abstract Book

S1238

ESTRO 37

metal material in proton treatment plan. However, density override with actual material of the fiducial marker could make problem such as inaccurate target contouring and compensator fabrication. Therefore, we perform density override with surrounding material instead of actual material and we intend to evaluate the usefulness of density override with surrounding material of the fiducial marker by analyzing the dose distribution according to the position, material of the fiducial marker We supposed that the fiducial marker of gold, steel, titanium is located in 1.5, 2.5, 4.0, 6.0 cm from the proton beam’s end of range using water phantom. Treatment plans were created by applying density override with the surrounding material and actual material of the fiducial marker. Also, a liver cancer patient who received proton therapy was selected. We located the fiducial marker of gold, steel, titanium in 0, 1.5, 3.5 cm from the proton beam’s end of range and the treatment plans were created by same method with water phantom. Homogeneity Index(HI), Conformity Index(CI) and maximum dose of Organ At Risk(OAR) in Planning Target Volume(PTV) as the evaluation index were compared according to the material, position of the fiducial marker and number of beam. Results The HI value was more decreased when density override with surrounding material of the fiducial marker was performed comparing with density override with actual material. Especially the HI value was increased when the fiducial marker was located farther from the proton beam's end of the range for a single beam and the fiducial marker's position was closer to isocenter for two or more beams. The CI value was close to 1 and OAR maximum dose was greatly reduced when density override with surrounding material of the fiducial marker was performed comparing with density override with actual material. Conclusion Density override with surrounding material can be expected to achieve more precise proton therapy than density override with actual material of the fiducial marker and could increase the dose uniformity and target coverage and reduce the dose to surrounding normal tissues for the small fiducial markers used in clinical practice. Most of all, it is desirable to plan the treatment by avoiding the fiducial marker of metal material as much as possible. However, if the fiducial marker have on the beam path, density override of the surrounding material can be expected to achieve more precise proton therapy. EP-2366 A new IMRT template for early stage Hodgkin’s Lymphoma: the 5 fields Sectorial Sliding Window IMRT S. Cornacchia 1 , A. Errico 2 , R. Errico 1 , E. Pierpaoli 1 , G. Guglielmi 3 1 Ospedale dimiccoli, Diagnostic imaging, Barletta, Italy 2 Ospedale dimiccoli, oncohematology, Barletta, Italy 3 university of Foggia, Department of Radiology, FOGGIA, Italy Purpose or Objective Patients with early stage Hodgkin’s Lymphoma (HL) are currently treated with 3D Conformal Radiation Therapy (CRT) and Intensity Modulated Radiation Therapy (IMRT) techniques, depending on staff assessment. The IMRT templates are used for sparing dose to heart and lungs, and number of beams. Material and Methods

rectum and to healthy tissue compared to 7F-I. Comparing the two VMAT techniques, R 50% and MU were slightly lower in 2A-V, but irradiation time was shorter in 1A-V, meaning that this treatment was more efficient, and could minimize patient movements during RT. EP-2364 Hippocampal sparing radiotherapy in primary brain tumors using volumetric modulated arc therapy M. Konopka-Filippow 1 , E. Sierko 1 , D. Hempel 1 , E. Szewczuk 2 , T. Filipowski 3 , M.Z. Wojtukiewicz 1 1 Medical University of Bialystok- Poland, Department of Clinical Oncology, Bialystok, Poland 2 Comprehensive Cancer Center in Bialystok- Poland, Department of Medical Physic, Bialystok, Poland 3 Comprehensive Cancer Center in Bialystok- Poland, Department of Radiotherapy-, Bialystok, Poland Purpose or Objective Sparing hippocampus during brain irradiation could avoid damage of neural progenitor cells located in subgranular zone of the hippocampus and subsequently avoid neurocognitive decline. The aim of the study was to asses the possibility of the reduction of radiation dose to contralateral or bilateral hippocampi in patients with primary malignant brain tumors using planning RT system and volumetric modulated arc therapy (VMAT). Material and Methods The study assigned 15 patients with high grade glial tumors (HGGT) III or IV WHO who received radiotherapy (VMAT) or 3D conformal RT (60 Gy in 30 fractions). Depending on tumor location contralateral or both hippocampi were delineated. RT plans were optimized to reduce the doses to hippocampus with maintaining the plan's acceptability parameters. Hippocampal dose and treatment parameters of VMAT plans were compared to the 3D conformal RT plans. Results All RT plans achieved PTV coverage of at least 95%. Average volume of delineated hippocampi was 5,2 cm 3 . Using VMAT technique median dose D 100% to the contraleral hippocampus was less than 16 Gy (10,8 Gy), whereas the maximal dose to the contralateral hippocampus was 15,8 Gy and ipsilateral - 23 Gy. VMAT technique allowed for median dose reduction to contralateral hippocampus by 28% comparing to 3D conformal RT plans. The total treatment RT fraction time was reduced by 4 min in VMAT technique vs 3D conformal. In 85 % cases there was no technical possibility for spare ipsilateral hippocampus, maintainly in centrally, large tumor location. Conclusion VMAT RT is feasible and might provide substantial reduction of the dose to contralateral hippocampus in HGGT. Large, centrally located tumors makes impossible excluded to spare both hippocampi and in some cases even contralateral. Sparing hippocampus in patients with glioblastoma in relation to neurocognitive toxicity needs to be investigated in the further studies. EP-2365 Comparing the dosimetric impact of fiducial marker according to density override method D.Y. Sung 1 , S.J. PARK 1 , J.H. PAKR 1 , Y.C. PARK 1 , H.C. Park 1 , B.K. Choi 1 1 Samsung Medical Center, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective The application of density override is very important to minimize dose calculation errors by fiducial markers of